NAND type flash memory has been recognize as a nonvolatile semiconductor memory device that can be rewritten and can be highly integrated. A memory transistor of a conventional NAND type flash memory has a stack gate structure formed by laminating an electric-charge accumulation layer (known as the floating gate) and a control gate with an insulation film disposed in between. In recent years, a NAND type flash memory structure for reliably maintaining the coupling ratio has been proposed where the potential of a write-in target memory cell is raised by placing a control gate electrode between adjacent floating gates along the word line direction, in place of the stack gate structure. Such structures have been proposed for reliably maintaining the coupling ratio without increasing the difficulty in processing by too much.